Bizarre ZMAIL/UNIX interaction problem

[delaney@xn.ll.mit.edu (John R. Delaney)]

This one is REALLY obscure, so pardon me if it takes a while to describe.

We have a network of 12 3600-class Symbolics machines, 1 MacIvory, and 20
SUNs. One SUN is our gateway to the Internet and holds all mail spool
files. The Symbolics namespace is set up so that one SUN is the only
STORE-AND-FORWARD host and all users have that SUN as their mail host. As a
matter of policy, other mail storage files are kept on the SUNs. That is,
every Symbolics user is assigned a SUN to keep such files (along with a
.login file, etc.). NFS on the SUNs makes all their file-systems look like
one, but users are still expected to log in primarily on the host holding
their .login file. So I am expected to log in on HOST-A and my mail file
(in my ZMAIL-INIT file) is in HOST-A:/home/host-a/delaney/mail/RMAIL while
my spool file is (effectively) in HOST-A:/usr/spool/mail/delaney. I have no
problem reading my mail from any of the 3600s or from the MacIvory,
although the latter prompts me for my SUN password 3 time while the former
does so only once. 

But then there is USER-C. He is assigned to HOST-V; his login file is
HOST-V:/home/host-v/user-c/.login and his mail file is
HOST-V:/home/host-v/user-c/RMAIL. But if he uses that in his ZMAIL-INIT
file, HOST-V rejects his attempts to login in from ZMAIL after prompting
for his password. If he uses HOST-A:/home/host-v/user-c/RMAIL instead in
his ZMAIL-INIT file, he has no problem. To make things more peculiar, if he
use the terminal emulator to connect to HOST-V, it accepts his login and
password fine. If he does EXECUTE COMMAND HOST-V PWD in the LISP Listener,
he get prompted for his password, but it is again accepted and prints the
right UNIX directory.

Further information: USER-C is the primary MacIvory user. I haven't tried
him yet on one of the 3600s; he is brand-new and has enough trouble with
the MacIvory. But I can do that if necessary to improve the diagnosis.

Other users with their .login and RMAIL files on HOST-V have no problems
with ZMAIL. For that matter, if I supply my SUN user name and then password
when USER-C is prompted for passwords, HOST-V also works OK.

Both HOST-A and HOST-V are run SUN OS release 4.0.3 (as are most of our
SUNs).

Any suggestions?

John